In an image forming apparatus, such as a printer and a copying machine, a sheet to be formed with an image is conveyed to an image forming part from a sheet feeding device. In the sheet feeding device, a pickup roller comes into contact with a downstream side end portion in a conveying direction of the sheet stored in a sheet feeding cassette, and then rotates to feed the uppermost sheet to the image forming part. In order to keep a feeding position where the pickup roller comes into contact with the uppermost sheet constant, an elevating plate on which the sheet is placed is supported so as to be inclined by a lift member. The lift member is turned around a rotating shaft by a drive unit to incline the elevating plate.
In addition, the sheet feeding device is sometimes configured to detect an amount of sheet placed on the elevating plate and then inform a user of a replenishment of sheets if necessary. In the above described sheet feeding device configured to incline the elevating plate, an inclining angle of the elevating plate, that is, an inclining angle of the lift plate is changed depending on the amount of sheets placed on the elevating plate. Based on the fact, a mechanism which detects a remaining amount of sheets by using the rotating angle of the rotating shaft of the lift member has been known. The mechanism for detecting a remaining amount of sheets will be described with reference to FIG. 6.
As shown in FIG. 6, the rotating shaft 101 of the lift member 100 is driven by the drive unit 102. The drive unit 102 includes a motor 103 and an output shaft 104 coupled to a motor shaft 103a of the motor 103 via gears. The rotating shaft 101 of the lift member 100 is coupled to an output shaft of the drive unit 102 by a joint member 105 so that they are integrally rotatable. To the rotating shaft 101 of the lift member 100, an actuator 107 having an approximately fan-like shape, as viewed from an axis direction of the rotating shaft 101, is provided so that they are integrally rotatable. In addition, within a rotation locus of the actuator 107 which is turned as the rotating shaft 101 is rotated, two sensors 108 and 109 which detect the actuator 107 are arranged at a predetermined interval at an upstream side and a downstream side. By turning the two sensors 108 and 109 into ON or OFF due to the rotating of the actuator 107, a rotating angle of the rotating shaft is detected at a plurality of steps (for example, three steps).
In the Patent Document 1, an example of the sheet feeding device is disclosed. The sheet feeding device includes an indicating piece coupled to the gear provided to the rotating shaft of the lift member via gears. As the rotating shaft is rotated, a position of the indicating piece is changed to inform a user of a remaining amount of sheets.